Oxidized starch and method of preparing the same



Patented Aug. 5, 1952 'oXI mzEns'r-ARon AND METHOD-10F" ase-Annie THE SAME 'fpora'tio'n of Illinois NoI)iavvi'irrg; Applicationhugustfig 1949, 2 Serial No. 108, 22?- This invention relates to modified starch and more particularly itot'starch that has been; oxidized with periodic acid :to' modify the molecular structure thereof and to produce a product having new and valuable properties and being useful for a variety of purposes, especially for the warp sizing of'tex-tile yarns. The invention also a V I v M i g g g H I by shortening the'maincarbohydrate chain-1n relates to at :iprocess for-".preparing modified starch by the oxidation of starcnwithtperiodio acid under controlled "conditions, ,as set forth more fully he'r'einaftenz 1 Textile yarns are:='si'z'ed the purpose bf protecting them from abrasion during the weaving" operation. iwarp izin also increases the strengthf yarns. This increase in strength is most noticeable with low twist yarns a d less s ams. (este mprior to iw ealving'for and dextrin formation are not completely unevident with more highly twisted of the original unmodified starch. Y

such as cotton and spun rayon, ratherviscou's This film ties inthefiberiends and thuscha nges a fuzzy yarn into a relatively smooth one. Consequently, fewer fibers arerbroken'ofi byabrasion against th'eloom parts during weaving and there is less fisheddihgj finfthe loom; Thus'fanfincrease in weave" room production is achieved. In the case of smooth yarns,jsuch as continuous filament rayon yarn, less viscous'size mixes are used. These tend to produce thin; flexible films of size on the yarn which prevent broken filaments from sliding back 'alongthe yarn during weaving and producing, fu'zz-balls or birds nests, which eventually entangle (adjacent yarns and cause end breakage In addition to protecting the yarn during weaving, the size mustbe capable orbeing' removed, prior to dyeing; Without damage to the fabric. Unmodified. minercial starches ,,.such as thick-boiling ..'corn.'st""rch, are not readily desized after 'wea'vi This has led to the develop-. ment of thin-bur 1 searches, British gums, and dextrins. Thinebb'ili'ng starches are used primarily on cottons andare essentially products obtained by acid hydrolysis of starch inthe form of a wet slurry. British gums are used-extensively on spun rayon and are produced usually 'by roasting starch "(1; e.-heating it in the dry state, with only its natu-ralmoisture content) in the presence of traces or alkali. made by roasting starch in, th presence oi catalysts and/or tracescg v r Dextrins are While. the ifoigfilngl materials are somewhat more; readily desnearmmthe fabric than raw starch they still usually requireftreatm'ent with enzymes. for satisfaclx'liily complete .removal. Also thejth'in-boilin'g starches have the disadvantage; thatiismee they are made by a hycroiyt ciproeess, increases "solubility is obtained the starch mo1'ecule.'..This leads to materials which have lower film "strength and greater brittleness and, consequently, are of less value in warp sizing. Although the mechanisms of gum derstood, it is a well known fact that highly converted materials of this sort have undergone considerable molecular degradation and their film's are weaker and more brittle than thos An object of the invention is to provide a modified starch that is especially suitable for Warp sizing of textile yarns and other sizing operations. Another object is to provide a modified or oxidized starch that has film-forming and adhesive properties similar 'to' those of unmodified starch but that exhibits a much greater ability to be dissolved or dispersed in dilute solutions of alkali. q I p Anotherjohj'ect is to provide "a modified starch for warp sizing 'a'nd like usesfthat maybe removed from the fabric; jafter weaving, with a rnild alkaline scour and without the use of agent;

enzymatic desizing preparations.

Another object of, the invention is to provide a process for the modification orjoxidation of starch utilizing periodic, ,a'cida's theloxidizing' The modifier-seats t the 'invention fmay be prepared from a wide variety of unmodified or partially modified starches. The following starting materialsmay- -be employedrraw corn Stal'Ch,.Am lOCa; starch which is a type of corn starch consisting-mainlyof-the branched chain fraction and-substantially, free-,from amylose, wheat starch, tapioca starch, potato starch, sago starch, thin-boiling ti e. acid-hydrolysed) starch' corn starches already =modified to some extent with alkaline hypochlorite and crude corn starches containing up to 3.5%;oi protein and some oil. f a

. he n oclified .--starches ;o-f the. invention 7 are characterized bylmany properties similar to those of the unmodified starting materials. Among these are t'(l-) a :g neralor superficial appearance tothe naked or unaided eye substantially identical -;'tp or; strongly resembling the unmodifiedstarting-material; (2) a grain structure as viewed under the microscope similar to that of the untreated starting material; (3) the showing of a polarization cross under polarized light that is typical of the cross-exhibited by the starting material; (4) a substantial reten- 5 tion of the highly polymeric structure or the unmodified starch; (5) the characteristic that pastes formed of the modified starch at normal pH (5 to '7 approximately) are substantially as viscous as those formed from the original starch and the film-forming properties and film characteristics such as flexibility, tensile strength and like physical properties are not substantially diminished in the products or the invention.

The modified starches of the invention have other properties that differ markedly from the corresponding properties of the starting materials. For example, alkaline solutions dissolve or dispersev the modified starches to a much greater extent and much more rapidly than they do the starting materials. I

' Although the invention is not dependent on the correctness of anytheory, it is believed that the molecular structure ofthe starch is changed by reaction of. the periodic acid withv a substantial number. oithe anhydroglucose units of the starch probably essentially as follows:

The conversion of two adjacent hydroxyl groups into aldehyde groups. although it opens the ring, does not break the main carbohydrate chain. However, opening the ring makes the compound especially sensitive to alkali so that treatment, even with mild alkali, tends to break the chain atthe carbon atoms once removed fromthe opening in ,the ring. Thus are produced starch derivatives, which at their normal pH values, (pH 5 to 7 approximately) are good film-forming materials. But the films, once formed, are readily dispersible or even soluble in alkali.

Additionally, the modified starches of the invention show greatly increased alkaline fluidity numbers and much decreased alkaline paste viscosities as compared with the starting materials.

Typically, the process of the invention includes suspending starch in an aqueous liquid and adding thereto periodic acid in an amount based on the dry weight or the starch ranging from about 0.05% to about 0.5% by weight calculated as HI04.2H20, and maintaining said periodic acid in contact with the starch at a pH of from about 4.5 to about 7.0 at'a temperature and for a time sufiicient to substantially completely react the periodic acid with the starch. Thereafter, the modified starch is preferably washed and dried. Particularly in the range of from about 0.1% to about 0.35% periodic acid, the resulting oxidized 7 ion of water.

starches exhibit excellent film-forming properties and greatly improved alkali resolubility or redisp bi y- In carrying out the processkoi' the invention, starch is slurried'in water'preferably at a concentration 01' approximately one pound per gal- The starch concentration is not critical and either more concentrated or more dilute slurries can be used. The only limitation is convenience in handling the mixture. If too concentrated a slurry is used it becomes diiiicult to stir the slurry sufliciently vigorously to insure uniform'mixing when the periodic acid solution is added. It too dilute slurries are used, dewatering or the starch after the reaction is complete involves the removal of larger volumes of water than necessary. The concentration of one pound of starch per gallon of water is convenient, but any concentration which can be handled satisfactorily is feasible. 1

The pH of the slurry is measuredand, i1 necessary, adjusted to a value? within the range'pH 4.5 to pH 7.0. A preferred working range is pH 4.5

to pH-6.0. Buffered acidic or basic solution may be used 'to adjust the pH to the desired value. The preferred pH range is close to that of commercial corn starch, that is, approximately pH 5.0, but somewhat higher or lower values can be used. It is inadvisable to workxat a'pH lower than about 4.5 because the starch molecule may be attacked hydrolytically by the acid rather than being oxidized. It. is notadvantageous to work above about pH 7.0 because of the comparatively slow'reaction rate and the low solubility of periodate salts.

Periodic acid is next added to the slurry, preferably in the form of a dilute aqueous solution and vigorous stirring is maintained so that the starch does not settle out of the slurry. Periodic acid is conveniently obtained as the dihydrate underthe name 01' paraperiodic acid The acid is in the form of deliquescent crystals and is therefore diflicult to-weigh accurately. In order to obviate this difficulty, solutions approximately 0.05 molal (11.4 g. HIO4.2H2O per liter of solution) are prepared and standardized. The amount of acid required for each preparation is then obtained by measuring out the correspond-, ing volume of solution.

The concentration 01' the added periodic acid solution is not critical, the more dilute the solution the greater the ease of thorough mixing of the reagent with the starch and the more uniform the product. However, solutions as concentrated as 0.5 molal (114 g. HIO4.2H1O per liter of solution) may be used-successfully. Solutions of concentrations lower than 0.05 molal. can also be used.

The addition 01 the periodic acid solution may, cause a slight lowering of the pH of the slurry,

The reaction is conveniently carried out at ordinary room temperatures of from about 15 C. to about 35 C., but the reaction proceeds well at temperatures as low as about 5 C. to as high as about C. The temperature, however, is not critical and temperatures above and below these limits may be used. In general, the higher the temperature, the more rapid the reaction rate.

Samples of the slurry undergoing reaction are withdrawn at intervals of approximately five minutes each and are tested for periodic acid in conventional manner. 1

When the test for periodic acid is no longer positive the reaction ,is substantially complete. At the concentrations of hydrogenion used and at room temperature,-appr'oximately C.-35 C., the periodic acid reacts very rapidly with the starch. ,The periodic acid usually reacts completely with the-starch less than ten minutes, and no positive tests for periodic acid are obtained after this time. However, to insure completereaction, the slurry is stirred for approximately 10 minutes after it shows a negative periodic acid test and then the modified starch is dewatered n any desired .or conventional way, as by filtering.

The modified starch filterzcake may be washed thoroughly in water to free it substantially from iodic acid as indicated by conventional testing procedures. I

If the test for. iodic acid is positive, therwhole filter cake is reslurriedin water, stirred vigorously for five minutes and then filtered a second time. This process is repeated until the filter cake ispractically free from iodic acid.

The filter cake is then broken. upand dried by any of the conventional means such .as .are used on raw or unmodified starch. The drying temperature and time should not bev such that the moist starch is gelatinized or the dry starch dextrinized. Air drying for at least 24 to 48 hours has been found satisfactory and convenient.

The lumps of dry starch are then pulverized and screened. Unless the degree of modifica tion is excessively high the lumps are found to powder readily and can be easily screened through a 100-mesh screen.

It will be obvious fromthe foregoing that by varying the amount of acid used in relation to a fixed amount of starch a series of modified starches can be prepared from any raw starch. These will differ mainly in their sensitivity to alkali, the more highly modified starches being more sensitive to alkali and their films being soluble or dispersible at lower pHs and lower temperatures; the less highly modified materials will be less sensitive to alkali and their films will require higher pHs and temperatures to dissolve or disperse them. Since the ease of des'izing is a function of the film solubility, it is seen that starches can be prepared with diiterent'desizing properties.

Alkaline fluidity Five g. starch, dry weight basis, are wet with 10 ml. of distilled water in a 250-ml. Pyrex beaker. At 25 C., 90 ml. of a 1% solutionor' NaOH are added with stirring, and the stirring is continued for 3 minutes from thetime th sodium hydroxide is poured in. .-fI he mixture is allowed to stand 2'7 min. more at 25C. At this time the contents are poured into-a standardized glass funnel with a special tip and the-quantity Consequently, products which can be desized under mild conditions-very dilute the degree of I by thisrtest.

of starch solution which runs from the funnel in 70 secs. at 25 C. is noted; "This amount, measured in vml.,.is taken as the fluidity, erg. the acidmodified thin-boiling starches of commerce with a fluidity of 40 will be fluid enough for 4.0 ml. of solution to pass the; funnel tip in 70 sec., with a fluidityof 60, .ml., etc. If 100: ml. water are poured intothe standard-tunnel at 325 C. 100 .ml. will. be delivered ii sec. Relatively, then, watermight be said to have a'fiuidity of .100 ml.

EXAMPLE I. 1

O-aidatidmntmm comEstdrah unth periodic acid inpresencerof bufier 181. g. .raw corn starch] (-Globe Pearl-moisture content -.10.4 is addedto 1468 ml. buffer and stirred vigorously at room temperature with a mechanical stirrer so that the starch does not setItlIe out. The ,pl lofthestarch in buffer slurry is 2.

A suitable'buffer .is made-by dissolving .5 g; sodium acetate (CI-Is.COONa.3HzO-molecular weight;=136.09) and 2.0g. glacial acetic acid (CHz.COOHmolecu1ar weight =60;05) in water and diluting to afinal volume of one liter. This gives a solution approximately 0.033..-molal in sodium acetate and 0.033 molal in acetic acid. The pH of the buffer solution is 4.7.

In these'examples, a volume of bufier solution is taken so that the combined'volume of buffer plus that oi'the added acidis such that the starch concentration is approximately-one lb. per gallon of-added liquid. This-concentration is determined fromthe weight of the starch as is and the moisture content is ignored in calculating the amount of added liquid.

To the starch in bufierslurry is added gradually 40 ml. of a 0.0498 molal solution of periodic acid. Stirring is continued during the addition of acid and for 15 minutes thereaften. Atthe end of that time the. test for periodic acid is negative and the pH .of the, slurry is 4.70. The slurry Film Solubility"...

is filtered by suction on a Biichne'r funnel and the filter cake is thoroughly washed with water. The cake is resuspended in water, stirred vigorously for five minutes, and filtered a second time. This operation is repeated a third time. The filter cake is then free oi iodic acid and-.iodates, and has a pH of 5.45.

The filter cakeyis broken into small pieces and allowed to air-dry for several-days. The lumps are broken up by gentle manual grinding with a mortar .and pestle and the starch screened through a ZOO-mesh screen. The'product is a fine, whit powder resembling starch in appearance. Weight of product'is175 g. with a mois turecontent of 9.9%. i

Properties 1 Original Starch V Oxidized Starch Alkaline Fluidity.- 0.7. 50.0. 1m Strength p.s.i 8,800 7,100 (81% of original film strength). At pH 9.6 and above and C. films dis- Films do not dissolve at pH 11.5

and l00 C., integrate into small but break into fragments which diminish in. size as temperature is raised. Practically completely dissolved at pH 9.6 and C; 21.4 mlp. (pH 5.45).

5-6 approx.

largeiragments.

percent.

Omidatioh of Amioca starch with periodic acid in presence 'orbufler 181 g. Amioca starch (11.8% moisture) is slurried in- 1467 ml. sodium'ac'etat'e-acetic' acid buffer. Thisis -treated -at room temperature with a mixture of 20.33 mi. 0.0492 molal periodic acid an'd 20.33 ml. water, th'e'mixture being adjusted to approximately pH 6.5 with a small amount of sodium bicarbonate. The rest of the procedure is the same as in Example I. The pH of the reaction mixture, measured immediately after the addition of the periodic acid and at the end of the reaction, is 4.7. After minutes there is no positive testv for periodic' acid, and the starch is filtered from the slurry as in Example I, washed, reslurried, and filtered twice. At the end of this time it is free from iodic acid and iodates. The pH of the filter cake is 5.7. It is allowed to airdry for several days. Then it is ground as in Example I and screened through a 100-mesh screen.

The product resembles the original Amioca except that it has a somewhat moregranular appearance. Its moisture content is 12.9 and its properties are tabulated below': 7

Properties Original Starch Oxidized Starch Alkaline Fluidity.

Film strengtl1 .'.p. s. i 5,900

Film solubility Dis'solves at pH 7.5 Dissolves at" pH 7.5

adso ss o; 1 and600. I

Oxidation of wheat starch with periodic acid in presence of bufler' 185.4 g: commercial wheat starch (12.6% moisture) is slurried in 1488 ml. sodium acetateacetic acid buffer. To this is added at room temperature 20.33 ml. of 0.0492 molal periodic acid. Measurements of pH are as follows: I

(1) Bufier so1ution-4.7

(2) Starch slurry'in buffer- 4.7

(3) Starch slurry in buffer after acid-4.69

(4) Starch slurry in buffer afteraddition of acid 15 minutes later4.68

addition of Property Original Starch Oxidized Starch Alkaline fluidity..." 2.8 53.0.

Film strength .p. 5. LV 7,600 7,100.

Film solubility Does not dissolve Soluble at 95 C. and

but breaks merely pH 10.5 and at into fragments at higher pH's and polg 131.5 and 95- temperatures.

.8 EXAMPLE'IV Oxidation of tapioca starch with periodic acid in bufier 182.4 g. tapioca starch (Best Maris grade; 11.2% moisture) is slurried in 1386 ml. sodium acetate-acetic acid buffer at approximately pH 4.5. A mixture of 40.7 ml. 0.0492 molal periodic acid and 81.4 ml. water is adjusted to pH 4.7

' ture (24 with sodium bicarbonate and then added to the starch slurry at room temperature. The mixture is stirred vigorously with a mechanical stirrer. The pH of the mixture immediately after addition of the periodic acid is 4.7 and remains at this value during the reaction. I

The mixture is stirred for 15 minutes after the addition of acid. At the end of seven minutes the test for periodic acid is negative, but stirring is continued until the end of the 15-minute period.

The product is then dewatered by suction as in the previous examples. After three flltrations the filter cake is found to be free from iodic acid and its final pH is 5.65. The starch is allowed to air-dry for 3 days. It is powdered and screened through a 100-mesh screen. Weight of product obtained is 186.0 g. at 15.3% moisture content.

Properties Original Starch Oxidized Starch Alkaline fluidity 2.8 68.5. Film strength p. s i... 6400. Film solubility Films do not dis- Films dissolve at pH solve at pH 11.5 7.5 and 75-80 C. and -l00 0.

EXAMPLE V Oxidation of corn starch in absence of buyer 179.4 g. of a crude corn starch (containing 1.23% protein and 9.7% moisture) is slurried in 1486 ml. distilled water and the pH of the mixture adjusted to pH 6.53 with 0.8 ml. 6-normal acetic acid. To this is added at room tempera- C.) 22.4 ml. of 0.0447 molal periodic acid. The mixture is stirred for 20 minutes. At

the end of this period the test for periodic acid is negative and the pH value has fallen to 6.37. The oxidized starch is recovered by filtration as in the preceding examples. Three filtrations are required to obtain a product free from iodic acid. The pH of the final filter cake is 7.04. The prodnet is allowed to air-dry for several days. Its weight is 192 grams with moisture content 18.0%.

Properties Original Starch i Oxidized Starch Alkaline fluidity 0.3 42.3.

Film strength.p. S. i. 4000 3500.

Film solubility Does not dissolve at Does not dissolve pH 11.5 and 9a but at pfl 7.5 and 0.; breaks inroom temperature to large fragments. breaks into fragments which become very small as pH and temperav tare are raised. 1

amples can be obtained by varying the amount of acid used for a given amount of starch.

In accordance with the invention, starches are oxidized. to provide modified starches having alkaline fluidities by the Kerr method ranging from about 30 to about 90, the products having the most useful properties ranging in alkaline fluidity from about 40 to about '70.

I claim:

1. Oxidized starch dispersible in water to form highly viscous water pastes and slurries at about pH to about pH 7 from which are deposited films having good flexibility and high tensile strength and which are readily dispersible in alkaline solutions, said oxidized starch having an alkaline fluidity ranging from about 30 to about 90, said oxidized starch being prepared by a process comprising reacting starch in an aqueous liquid medium with periodic acid in an amount ranging from about 0.05 part to about 0.5 part by weight for each 100 parts by weight of dry starch, calculated as HIO4.2H2O, at a pH of from about 4.5 to about 7.0 at a temperature and for a time suilicient to substantially completely react the periodic acidwith the starch.

2. The method of oxidizing starch to increase the alkali solubility thereof which comprises reacting starch in an aqueous liquid medium with periodic acid in an amount ranging from about 0.05 part to about 0.5 part by weight for each 100 parts by weight of dry starch, calculated as H104.2H2O, at a pH of from about 4.5 to about 7.0 at a temperature and for a time sufficient to substantially completely react the periodic acid with the starch.

3. The method of oxidizing starch to increase the alkali solubility thereof which comprises reacting starch in an aqueous liquid medium with periodic acid in an amount ranging from about 0.1 part to about 0.35 part by weight for each 100 parts by weight of dry starch, calculated as I-IIO4.2I-I2O, at a pH of from about 4.5 to about 7.0 at a temperature and for a time sufiicient to substantially completely react the periodic acid with the starch.

4. The method of oxidizing starch to increase the alkali solubility thereof which comprises reacting starch in an aqueous liquid medium with periodic acid in an amount ranging from about 0.1 part to about 0.35 part by weight for each parts by weight of dry starch, calculated as HIO42H2O, at a pH of from about 4.5 to about 6.0 at a temperature and for a time sufiicient to substantially completely react the periodic acid with the starch.

5. The method of oxidizing starch to increase the alkali solubility thereof which comprises reacting starch in an aqueous liquid medium at a concentration of about '1 lb. of starch per gallon of liquid with periodic acid in an amount ranging from about 0.1 part to about 0.35 part by weight for each 100 parts by weight of dry starch, calculated as HIO42H2O, at a pH of from about 4.5 to about 6.0 at a temperature of from about 15 C. to about 35 C. and for a time suificient to substantially completely react the periodic acid with the starch.

WILLIAM E. C. YELLAND.

REFERENCES CITED The following references are of record in the file of this patent:

Chem. Abstracts, vol. 32, page 5280*, 1938.

Chem. Abstracts, vol. 32, page 5246 1938.

Chem. Abstracts, vol. 32, page 825 1938.

Grangaard et al., Paper Trade Journal, vol. 115, No. 7, August 13, 1942, pages 41-46.

Carbohydrate Chemistry by Goepp, 1948, pages 581 and 582. 

1. OXIDIZED STARCH DISPERSIBLE IN WATER TO FORM HIGHLY VISCOUS WATER PASTES AND SLURRIES AT ABOUT PH 5 T ABOUT PH 7 FROM WHICH ARE DEPOSITED FILMS HAVING GOOD FLEXIBILITY AND HIGH TENSILE STRENGTH AND WHICH ARE READILY DISPERSIBLE IN ALKALINE SOLUTIONS, SAID OXIDIZED STARCH HAVING AN ALKALINE FLUIDITY RANGING FROM ABOUT 30 TO ABOUT 90, SAID OXIDIZED STARCH BEING PREPARED BY A PROCESS COMPRISING REACTING STARCH IN AN AQUEOUS LIQUID MEDIUM WITH PERIODIC ACID IN AN AMOUNT RANGING FROM ABOUT 0.05 PART TO ABOUT 0.5 PART BY WEIGHT FOR EACH 100 PARTS BY WEIGHT OF DRY STARCH, CALCULATED AS HIO4.2H2O, AT A PH OF FROM ABOUT 4.5 TO ABOUT 7.0 AT A TEMPERATURE AND FOR A TIME SUFFICIENT TO SUBSTANTIALLY COMPLETELY REACT THE PERIODIC ACID WITH THE STARCH. 